Gas turbines comprise a casing for housing a compressor section, combustion section and turbine section. The combustion section comprises an inlet end, a discharge end and a combustor transition. The transition, which is simply a duct, is proximate the discharge end of the combustion section and comprises a wall that defines a flow channel that directs the working fluid into the turbine inlet end.
A supply of air is compressed in the compressor section and directed into the combustion section. The compressed air enters the combustion inlet and is mixed with fuel. The air/fuel mixture is then combusted to produce high temperature and high pressure gas. This gas is then directed through the transition and into the turbine section, where it forms the turbine working fluid. The gas flows over the blades of the turbine, which causes the turbine rotor to drive a generator, thereby producing electricity.
As those skilled in the art are aware, the maximum power output of a gas turbine is achieved by heating the gas flowing through the combustion section to as high a temperature as is feasible. The hot gas, which is also at a high pressure, heats the various turbine components as it flows through the turbine. Accordingly, the ability to increase the combustion firing temperature is limited by the ability of the turbine components to withstand the increased temperature and pressure of the gas.
FIG. 1 shows a side view of a combustion section of a gas turbine. As is typical, the combustion section comprises a number of combustors (or combustion baskets) 10 in which the air/fuel mixture is burned. Shown in FIG. 2 is an exploded perspective view of the connection of the combustor basket 10 to the transition 30. The combustor basket 10 is connected to the transition 30 by means of a transition cylinder 20. The upstream end 22 of the cylinder 20 slides onto an outlet end 12 of the combustor basket 10 and the downstream end 28 of the cylinder 20 is mechanically coupled to an upstream end 32 of the transition 30.
The cylinder 20 directs the hot gas from the combustor basket 10 into the upstream end 32 of the transition 30 and is best viewed as an extension of the transition 20. The cylinder 20 serves as an aid in servicing the turbine. If one did not have some way of separating the transition 30 from the combustor basket 10 one would have to pull the basket 10 completely out of the turbine before removing the transition 30 for servicing. The cylinder 20 allows for removal of the transition 30 without removing the combustor basket 10.
One common technique of attaching the cylinder 10 to the transition 30 is to utilize a "V" band coupling 40. The area of concern to the present invention as highlighted in FIG. 1 is depicted in FIG. 3. As shown in FIG. 3, there are respective mating flanges 24 and 34 on the downstream end 28 of cylinder 20 and the upstream end 32 of the transition 30, over which the "V" band coupling 40 fits.
The "V" band coupling 40 comprises two semi-circular rings, each of which surround 180 degrees of the junction of the mating flanges 24 and 34. The rings of the "V" band coupling 40 are bolted together where the mating flanges 24 and 34 meet. This bolting mechanism is intended to clamp the "V" band coupling 40 radially inward around the respective mating flanges 24 and 34 of the cylinder 20 and the transition 30, thereby holding these parts in position while maintaining their integrity.
The "V" band coupling 40 technique, however, has several drawbacks. One such drawback is that the mating flanges 24 and 34 do not have a direct mechanical coupling to prevent fretting caused by the vibration forces of the combustor and the turbulent conditions of the gas exiting the combustor basket 10. As a result, the parts of the cylinder 20 and transition 30 that contact each other, i.e., the respective faces 25 and 35 of the mating flanges 24 and 34, are susceptible to such fretting.
Another drawback of the "V" band coupling 40 is that its clamping design is not strong enough for its intended purpose. The "V" band coupling 40 has been found to be too weak to withstand the forces caused by thermal expansion. As a result, the coupling 40 yields and becomes loose which causes fretting of the surfaces 25 and 35 of the mating flanges 24 and 34. It is, therefore, desirable to provide an apparatus for connecting a transition cylinder to a transition of a gas turbine that is more robust and is less susceptible to fretting than conventional apparatus.